The invention is related to clutching devices generally and more specifically to an engine driven apparatus for driving at least one vehicle mounted accessory at either one of two selectable speeds as well as being able to totally disengage (zero speed) the accesory.
Planetary gear sets are often used in drive units for speed changing applications by selectively restraining one of either the ring gear, the sun gear or the planet gear carrier. One such drive unit is illustrated in U.S. Pat. No. 2,959,070. In the context of an accessory drive unit for automotive applications the planet gear set may be employed as a means for driving the accessory at a speed that is different from the speed of the engine (crankshaft). Overdriving the accessory, that is, to drive it faster than the speed of the engine reduces the useful life of the gear unit and often generates an unacceptable level of accoustic whine. Further, prior drive units have used planetary gear sets to drive the accessory at only either of two speeds. The first speed being equal to input speed and the second speed differing from the first by the effective gear ratio of the gear set. It is desirable and often a necessity with smaller displacement engines to be able to disengage the accessories when starting the vehicle. This feature is especially important during cold start to lessen the drag on the engine.
It is an object of the present invention to provide an engine driven, clutched drive capable of driving a belt driven accessory to full speed, reduced speed and zero speed (disengaged). A further object is to provide such a device utilizing a speed reducing planetary gear set. An additional object of the present invention is to provide means for performing the clutching function in a simple manner. Many other objects and purposes of the invention will become apparent from the detailed description.
Accordingly the invention is directed to:
A multi-speed accessory drive having a plurality of operating conditions in which an output member is rotated at the speed of an input or driving member, at a reduced speed ratio or at zero speed comprising: a pressure plate axially movable relative to the input member, and a driving link rotatably fixed to the input member and to the pressure plate for rotating the pressure plate and for axially urging the pressure plate away from the driving link. The drive further includes means for moving the pressure plate into contact with and for rotational engagement with the output member and for alternatively drivingly connecting the output member to the input member; and means for disengaging the ring gear of the planetary gear set during intervals when the pressure plate is in engagement with the output member to permit the output member to rotate at the speed of the input member, for halting the rotation of the ring gear when the pressure plate is disengaged from the output member to permit the output member to rotate at a predetermined ratio of the speed of the input member and for disengaging the ring gear during intervals when the pressure plate is disengaged from the output member thereby permitting said output member to remain stationary while the input rotates.